The instant invention relates to the formation of extruded metal containers and more particularly to a method and apparatus for forming an extruded metal tube having a substantially flat, closed, end wall and a projection which extends integrally from the end wall.
It is generally recognized that it is possible to effectively extrude certain metals, such as aluminum, to form relatively thin-walled tubular elements and canisters for use in packaging various types of goods. In this regard, extruded tubular metal containers have been effectively utilized for a number of years for packaging various materials, including epoxies and other adhesives, toothpaste, and certain food products. Extruded metal tubes having slightly greater wall thicknesses have also been effectively utilized for containing and packaging various pressurized materials, including propane, butane, and various tear gasses.
The most widely accepted technique for forming thin walled tubular members of the above type is to assemble a predetermined quantity of a solid extrudable metal in a die and to then apply a punch to the metal in the die with a sufficient force to liquify the metal so that it is extruded through the areas between the punch and the die. In this regard, a die utilized in an operation of this type generally comprises a pair of die elements which cooperate to define a substantially closed-ended cylindrical recess. The first of these die elements is generally adapted to define the substantially closed terminal end portions of the recess, and it may include a vent opening for venting gases which are generated during an extrusion operation. The second of these die elements is generally formed in a ring-like configuration and adapted to be received on the first die element so that it provides a tubular extension of the portions of the recess formed in the first die element. The punch of a punch and die assembly of this type is generally formed in a configuration which is complimentary to that of the recess but in a slightly smaller dimension than the recess. Accordingly, by assembling a quantity of an extrudable metal in the recess and then advancing the punch into the recess with an extremely high force, it is possible to liquify the extrudable metal. Further, since a liquified metal under extremely high pressure always follows a path of least resistance, it is possible to extrude the metal outwardly from the recess along the sides of the punch to form a thin-walled metal tube.
While the previously known metal extrusion techniques of the above described type have generally been found to be effective for forming extruded tubular metal containers having flat end walls, conical end walls, or conical end walls with projections thereon, heretofore it has generally not been possible to form extruded tubular metal containers having substantially flat end walls and projections which extend outwardly from the end walls thereof. In this regard, it is generally recognized that containers having conical end walls or even containers, such as dispenser tubes, having conical end walls with threaded terminal projections thereon, can be effectively formed utilizing correspondingly formed extrusion dies and punches. However, this is because the angular end walls of the dies and the complimentary angular end walls of the punches utilized for extrusion operations of this type are capable of cooperating to cause liquified metal to flow along the angular surfaces of the punches and dies. Accordingly, when utilizing punches and corresponding dies having angular end walls it is possible to cause metal to flow into terminal cavities in the dies in addition to causing liquified metal to flow outwardly along the cylindrical surfaces of the respective punches. However, when forming containers having substantially flat end walls which are substantially perpendicular to the cylindrical side walls thereof, liquified metals tend to more readily flow outwardly along the cylindrical surfaces of punches rather than into terminal cavities in corresponding dies. This is particularly true when forming tubular members having relatively high side wall thickness, such as those having side wall thickness of greater than approximately 0.01 inch due to the increased spacing required between punches and the respective dies therefore. Accordingly, because of the tendency of highly pressurized liquified metals to inherently seek paths of least resistance, which, when utilizing dies having flat end walls, is outwardly along the sides of the punches thereof, heretofore it has not been possible to form projections or the like on the end walls of extruded metal containers having substantially flat end walls which are perpendicular to the respective side walls thereof.
The instant invention provides an effective method and apparatus for forming extruded metal containers having tubular side walls, substantially flat end walls which are substantially perpendicular to the respective side walls thereof and integrally formed projections which extend outwardly from the respective end walls thereof. More specifically, in accordance with the method of the instant invention, a cylindrical extruded metal tube having a closed end wall which is substantially perpendicular to the side wall thereof and having a projection which extends integrally from the end wall is formed by first assembling an extrudable metal disc in a recess in a die. The recess is formed in a configuration which is complimentary to the terminal end portion of the desired tube, and hence, it has a side wall, a substantially flat end wall which is substantially perpendicular to the side wall and a cavity which is positioned and configured to correspond to the position and configuration of the desired terminal projection on the metal tube. The cavity preferably also has a vent hole therein for venting gases formed or displaced from the recess in the die during an extrusion process. The next step in the method comprises applying a substantially cylindrical punch to the disc in the recess in order to liquify the metal in the disc and to extrude the liquified metal outwardly along the sides of the punch and also into the cavity. The punch utilized in the method has a longitudinally extending side wall and an end face including a peripheral portion which is substantially symmetrical about the axis of the punch. The peripheral portion is formed at an angle of between approximately 10.degree. and 20.degree. relative to a plane which is perpendicular to the axis of the punch so that the peripheral portion of the end wall of the punch angles outwardly and backwardly relative to the center portion of the end wall. The peripheral portion of the end wall merges with a slightly enlarged outer rim portion formed at the terminal end of the side wall of the punch. The outer rim portion has a diameter which is less than the diameter of the recess in the die by an amount equal to the desired thickness of the side wall of the tubular member formed by the method. The punch is applied to the metal disc in the recess in the die with a sufficient force to liquify the metal in the disc and to extrude the liquified metal outwardly between the rim portion of the punch and the side wall of the die so that the metal passes upwardly along the longitudinal extent of the punch. However, because of the angular configuration of the peripheral portion of the end wall of the punch, a certain amount of the liquified metal from the extrudable disc is also extruded into the cavity in the die to form an integral projection on the end wall of the tubular member.
The method of the subject invention is preferably carried out utilizing a punch having a center portion which is preferably substantially perpendicular to the axis of the punch, and the peripheral portion extends angularly outwardly from the center portion. Further, the cavity in the die preferably has a generally tapered triangular configuration, and it includes a pair of spaced side faces which converge slightly in their outward extents.
Accordingly, it is seen that the instant invention provides an effective method and apparatus for forming an extruded tubular metal container having a substantially flat end wall and a projection which extends integrally from the end wall. In this regard, while it is recognized that it is generally impossible to form an extruded tubular metal container having a substantially flat end wall and a projection which extends outwardly from the end wall by conventional extrusion techniques which utilize both punches and dies having substantially flat end walls thereon, it has now been found that it is possible to form a tubular container of this type utilizing a punch having an end wall which includes an angularly disposed peripheral portion and a die having a substantially flat end wall. Specifically, it has been found that by utilizing a die and punch assembly of this type it is possible to extrude a certain quantity of the extrudable liquified metal which would normally flow outwardly between the side walls of the punch and the die so that the metal instead passes into a cavity formed in the end wall of the die. In this regard, it has generally been found that as the angle of the peripheral portion of the end wall of a punch is decreased, the amount of force required to force metal into a cavity in the recess in a die is increased, and that it is virtually impossible to force metal into a terminal cavity when the angle of the peripheral portion of the punch is significantly less than approximately 10.degree.. On the other hand, as the angle of the end portion of the end wall of a punch is increased beyond approximately 20.degree., the thickness of the peripheral portion of the end wall of a container formed by the method becomes so great that increased material costs make the method impractical.
Accordingly, it is primary object of the instant invention is to provide a method of forming an extruded tubular member having a substantially flat end wall and an integrally formed projection on the end wall.
Another object of the instant invention is to provide a punch and die assembly for forming an extruded tubular member having a substantially flat end wall and a projection which extends outwardly from the end wall.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.